7.3 Structure and Role of the Processor and its Components

Question 1

What do processors contain ?

Answer 1

ALU, a control unit and
numerous registers.

Question 2

What is the role of the ALU ?

Answer 2

Perform arithmetic and
logic operations.

Question 3

What is the role of the Control Unit ?

Answer 3

controlling the various components of the processor and the Fetch-Execute Cycle .

Question 4

What are Registers ?

Answer 4

small storage locations used to hold data temporarily

Question 5

What are the characteristics of Registers ?

Answer 5

high read and write speeds.

Question 6

What are the 5 Special Purpose Registers ?

Answer 6

PC, CIR, MAR , MBR , SR

Question 7

What is the purpose of the Program Counter ?

Answer 7

Used to hold the memory address of the next
instruction to be executed in the fetch-execute cycle

Question 8

What is the purpose of the Current Instruction Register ?

Answer 8

Holds the instruction that is currently being executed
by the processor.

Question 9

What is the purpose of the Memory Address Register ?

Answer 9

Stores the memory address of a memory location that is to be read from or written to.

Question 10

What is the purpose of the Memory Buffer Register ?

Answer 10

Holds the contents of a memory location that has been read from or data that is to be stored

Question 11

What is the purpose of the Status Register ?

Answer 11

Contains a number of bits, the values of which can change to indicate the occurrence of an interrupt.

Question 12

What is the Role of the System Clock ?

Answer 12

Generates a timing signal
which changes at a regular frequency.

Question 13

What is the purpose of the signal generated by the System Clock ?

Answer 13

used to synchronise communication between the components of the processor and the rest of the computer system.

Question 14

What are the three stages of the Fetch - Execute Cycle ?

Answer 14

Fetch, decode and execute.

Question 15

What happens in the Fetch stage ?

Answer 15

The next instruction to execute is retrieved from main memory.

Question 16

What are the steps of the Fetch stage ?

Answer 16

1. The content of the PC is copied to the MAR
2. The content of the MAR is transferred to main memory by the address bus
3. The instruction is sent from main memory to the MBR by the data bus
4. The PC is incremented by one
5. The content of the MBR is copied to the CIR

Question 17

What happens in the Decode stage of the cycle ?

Answer 17

The fetched instruction is
decoded

Question 18

What are the steps of the Decode stage ?

Answer 18

1. The content of the CIR is decoded by the control unit
2. The decoded instruction is split into two parts: opcode
   and operands

Question 19

What happens in the Execute stage of the cycle ?

Answer 19

The instruction is carried out

Question 20

What are the steps of the Execute stage ?

Answer 20

1. Any data required by the instruction that isn’t present in registers is fetched
2. The instruction is carried out
3. Results of any calculations are stored in general purpose registers or main memory

Question 21

What happens between each execute and fetch stage of the cycle ?

Answer 21

Content of the status register is
checked for changes that could signify the occurrence of an interrupt.

Question 22

What is the Processor’s Instruction Set ?

Answer 22

the unique group of instructions that it can carry out

Question 23

What are the Instructions of the Processor’s Instruction Set stored in ?

Answer 23

Machine Code

Question 24

What are the two primary parts of the Instructions in the Processor’s Instruction Set ?

Answer 24

-Opcode
-Operands

Question 25

What is the opcode ?

Answer 25

type of operation that is to be carried out

Question 26

What is the operand ?

Answer 26

pieces of data on which the operation is performed.

Question 27

What two parts make up the opcode ?

Answer 27

- Operation - Addressing Mode

Question 28

How is the addressing mode specified in the opcode ?

Answer 28

One bit in a machine code instruction

Question 29

What are the two addressing modes ?

Answer 29

- Immediate - Direct

Question 30

What is effect of immediate addressing ?

Answer 30

the value specified in the operand is to be treated as the actual value

Question 31

What is effect of Direct addressing ?

Answer 31

The value specified by an operand signifies a memory address

Question 32

What is logical shifting ?

Answer 32

shifting all of the bits in a number

Question 33

What is an interrupt ?

Answer 33

A signal sent to the processor by another part of the computer requesting the attention of the processor

Question 34

Can Software also send Interrupts ?

Answer 34

Yes, eg. Division by Zero

Question 35

How are interrupts detected ?

Answer 35

change in the content of the status register

Question 36

How are interrupts handled ?

Answer 36

vectored interrupt method

Question 37

What is the Vectored interrupt method ?

Answer 37

processor stops executing the current program and places the content of its registers onto the system stack

Question 38

What is an interrupt service routine ?

Answer 38

A series of instructions for handling the interrupt that is specific to the type of interrupt.

Question 39

What are the factors that affect processor performance ?

Answer 39

Number of Cores, Cache Memory, Clock Speed , Word Length, Address Bus Width, Data Bus Width

Question 40

What is a Word ?

Answer 40

A group of bits that is treated as a single unit by a processor